The present work studies the removal of indigo carmine from aqueous solutions by an electrocoagulation (EC)/granular activated carbon (GAC) adsorption coupling process. The kinetics of this coupling process was studied using several GACs and different amounts of adsorbent material in order to identify the most appropriate adsorbent and dosage, respectively, for enhancing wastewater treatment. The influence of current density on the removal efficiency and electrical operating costs of the EC/GAC coupling process was also determined.
Four GAC materials, Pica F22, L27, X17 and S21, were characterized and used in the study of the EC/GAC coupling process. The textural characteristics of adsorbent materials were established based on nitrogen adsorption and their surface chemical properties were investigated by FTIR spectroscopy.

The coupling between electrocoagulation and GAC showed that the addition of an appropriate GAC resulted in the enhancement of the removal rate of indigo carmine especially at lower current densities, and in a considerable reduction in the contact time compared to the conventional simple EC process and simple adsorption process. Though the F22 exhibited outstanding adsorption properties related to indigo carmine dye, Pica L27/EC coupling provided the best rate constants.
Based on the significant decrease in electrical operating costs, the EC/GAC coupling method could be recommended instead of the conventional simple EC.